During the shutdown, the Accelerator Update will offer a series on the history and operation of the laboratory's accelerator complex. The Main Injector History is the eighth in a series.

The Main Injector (MI) is the fourth accelerator in the Fermi chain of accelerators. It takes 8 GeV protons from the Booster (through the MI-8 transfer line) and then accelerates the particles to 8 GeV, 120 GeV, or 150 GeV, depending on where they're going. MI can send protons and antiprotons to the Tevatron, protons to the Antiproton Source (Pbar), and protons to the Switchyard and Recycler. It receives antiprotons from Pbar and the Recycler.

MI is a 10,890-feet circumference proton/antiproton synchrotron. MI is made up of 552 magnets. Its tunnel is 8 feet high and 10 feet wide, covered by about 25 feet of earth shielding.

Accelerator History
Fermilab began building a superconducting accelerator, the Tevatron (TeV), in 1981. The magnets were installed below the Main Ring magnets. The Main Ring became a pre-accelerator for the TeV. Having both accelerators in the same tunnel saved millions of dollars in construction costs.

In 1984, Fermilab started conducting colliding beam physics, which allowed collisions that released more energy than any fixed target program could provide.

Fermi's protons come from a bottle of hydrogen gas. Unfortunately, antiprotons don't come so nicely packaged; they were created by striking a special target with protons. Originally, the Main Ring took care of all this proton antiproton manipulation, but not without a substantial loss in beam performance, quality, and data taking. As time went on, the limitations of the Main Ring became telling.

Eventually, Fermi scientists decided that they needed a separate machine, the Main Injector. It would be a smaller, faster, and more efficient version of the Main Ring, and would do everything Main Ring had done and additionally it could extract 120 GeV beam directly to the fixed target experiments.

In 1987, a group of physicists, interested in enhancing the performance of the Tevatron, began the initial designing. Construction started in 1993. By 1999, the Main Injector was ready for high energy physics.

Perhaps out of fear that building an accelerator with such a multitude of functions would not be sufficiently challenging, the scientists decided to add a second machine to the Main Injector tunnel. It would be known as the Recycler, because in its original conception, besides being a storage ring, it would have also salvaged unused antiprotons from the Tevatron once data taking was completed. That notion was dropped. The Recycler magnets are located directly above the Main Injector magnets. (More on the Recycler in a later report.)

The Main Injector

The Main Injector has about 15,000 feet of tunnel, eleven service buildings, and its own substation. It has 344 dipole magnets and 208 quadrupole magnets. The Main Injector covers approximately 440 acres of land and is elliptical in shape.